This application claims the priority of Korean Patent Application Nos. 2002-7439, filed on Feb. 8, 2002, and 2002-26269, filed on May 13, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an image processor, and more particularly, to a method and an apparatus for adjusting the brightness of an image while maintaining the hue and saturation of the image.
2. Description of the Related Art
As micro-displays, such as a liquid crystal display (LCD), liquid crystal on silicon (LCoS), or a digital micromirror device (DMD), or color displays, such as a plasma display panel (PDP), are widely used for computer monitors or television sets, their markets are getting bigger and bigger. High-power lamps or high-power electrodes have been employed in the displays in order to increase the amount of the output light of a display screen greater than the amount of the output light of a cathode ray tube.
A four-color display, in which an arbitrary color component (hereinafter, referred to as a fourth color component) is added to three conventional color components, referred to as first through third color components, has been developed in order to increase the brightness of an output image without using a high-power lamp or a high-power electrode. The fourth color component can be obtained by either letting light beams of a lamp in the display pass through a filter for a fourth color component (hereinafter, referred to as a fourth filter) or reflecting light beams with the fourth filter. When the fourth filter is a white filter, the brightness of a display can be increased, and thus there is no need to use a high-power lamp or a high-power electrode. Alternatively, if the fourth filter is an arbitrary color filter, the ability to represent colors in the corresponding color gamut can be enhanced, and thus it may be possible to represent colors of high quality in a display. Accordingly, it is necessary to extract a fourth color component from three color components, thus providing four color components.
One of conventional techniques of increasing the brightness of an output image is disclosed in U.S. Pat. No. 5,233,385, “White Light Enhanced Color Field Sequential Projection” to Texas Instruments Incorporated. In this method, a white filter is added to red, green, and blue (R, G, and B) filters. Then, it is possible to enhance the brightness of an output image proportional to the magnitude of a white filter section by a field sequential method, in which a white filter section or a white light frame is added to the R, G, and B filters after spatially dividing a filter section for generating colors by four or temporally dividing a video frame by four. However, even though this method can enhance the brightness of an output image in a display, it can lower the original saturation of pixels of the output image because an increase in the brightness of the output image is done with achromatic components.
There is another conventional technique of changing the brightness of an image, i.e., the disclosure presented in U.S. Pat. No. 5,929,843 “Image Processing Apparatus Which Extracts White Component Data” to Canon Kabushiki Kaisha. According to this method, a white component, which is extracted from each of R, G, and B data and is subjected to a halftone process, is transferred to R, G, and B filters and white display dots when red, green, blue, and white are determined as pixel units in a binary liquid crystal display. This method generates a white component by nonlinearly converting a minimum value among inputted R, G, and B data. In other words, a nonlinear model corresponds to gamma, offset, and scale. In short, this method reinforces a white component of the conventional field sequential method to be possibly applied to each pixel and determines how much a white component is applied to pixels by following a predetermined model. However, this method does not consider any means to maintain the original saturation of output images and to prevent color images from being achromatic due to the increase in the amount of a white component applied to pixels of the images. Accordingly, it is impossible to maintain the saturation of an image when increasing the brightness of an output image.